Studies will be made of a totally new observation, namely, the finding of a highly motile organism in the trophoblast of each of 38 consecutive trophoblastic tumors and not found in normal placentas or five other types of cancer. The organism is not yet identified and is still completely unknown to us and to our authoritative consultants. Methods in the initial phase will be obtaining more specimens, cell culture of trophoblastic tumors, phase contrast time lapse photomicrography, stationary phase contrast, light microscopy, scanning and E.M. microscopy, isolation and concentration of the organism, establishing axenic cultures of the organism, effect produced by injecting the organism in Balb/c mice, and possible modes of transmission; search of normal placentas in various stages of gestation; collaborative studies with the Laboratory of Parasitic Diseases, N.I.A.I.D. We will examine the non-specific, and the specific, cellular immune reactivity of the ptients' peripheral blood mononuclear cells taken before, during, and following successful therapy; examine the specific cellular immune reactivity against the father's antigens; and examine the non-specific, specific, and father specific cellular immune reactivity in peripheral blood mononuclear cells in patients with recurrent or resistant disease. Clinical trials of two new protocols in low risk and high risk disease and trials of new agents in patients who fail standard therapy or develop resistance will be conducted.